One of our members was kind enough to let me try-on this harness with Mac before purchasing it. As I am completely new to weight pull, I'm just wondering if the harness fits properly.

It's a little difficult to get over his big boulder-sized skull, but once it's over his head, the harness seems to just fall right into place on his shoulders. Mac is also very long-legged and has a very long stride (we're guessing he's mixed with Mastiff due to his huge size) -- his rear legs hit the bar when he tries to extend his stride, but I'm thinking he won't be running in the harness, so that really shouldn't matter?

What do you guys think?

As you can tell, he's not happy to be standing still for the photos and as soon as I put the harness on him and attached the leash so I could take pics, he leaned right into the shoulder straps and started pulling me across the yard, LOL. Maybe he's a natural?

Never make someone a priority in your life when that someone treats you like an option.

I'm just learning about proper fit. Most important is that the harness ride on their shoulders, w/out pressing on their windpipe. If they ride too high, you're basically choking the dog whenever he is working, which can be a deterrent to say the least.
Here's my pup just hanging out in a properly fitted harness.
Here she is working. She how it sits on her shoulders, distributing the weight w/out cutting into her airway.